1. Field of the Invention
The present invention relates to an image pickup equipment and method. More particularly, the present invention relates to an image pickup equipment and method in which degradation of an image can be prevented specifically when portions of high brightness and low brightness are included in each image.
2. Description Related to the Prior Art
A digital still camera is widely used as image pickup equipment, in which a CCD image sensor picks up an object image photoelectrically as image pickup device. However, a dynamic range of a digital still camera is smaller than that of a photographic camera for use with silver halide photosensitive material. An image picked up has comparatively low clarity and low gradation. To pick up and record the image of an object of low brightness, an image pickup signal output by the image pickup device is amplified at a predetermined coefficient to raise gain, so the image with clarity and high gradation can be acquired. However, this is unsuitable if portions of high the brightness and the low the brightness are included in the image, because of occurrence of local overexposure in the image due to amplification of the image pickup signal over a reproducible range of the gradation when an object of high brightness is photographed.
JP-A 5-007336, the image pickup equipment or digital camera is disclosed in which an object is photographed for plural times at different lengths of exposure time, and the obtained images are synthesized virtually to extend a dynamic range of the image pickup signal. JP-A 2004-363726 discloses the image pickup equipment in which a gamma conversion table is determined according to a gradation level of the brightness of the image obtained by the image pickup device or CCD, and the gradation level is converted according the gamma conversion table so that an gradient of a characteristic of an output and input of the gradation level is determined high in a principal object range of low brightness assigned to a principal object. The gradient of a characteristic of an output and input of the gradation level is determined high in a principal object range of high brightness.
However, the image pickup equipment or digital camera in JP-A 5-007336 synthesizes the image of plural periods after consecutively photographing the same scene at different exposure levels. This idea is not suitable for a moving object, such as a human being. In the image pickup equipment of JP-A 2004-363726, the gamma conversion table is changed according to evaluating information of high brightness. However, there is a problem in complexity in controlling the exposure because determination of optimized exposure is required, to lower a speed of processing.